Recent epidemiological surveys have shown a reduction in dental caries in children, while highlighting the problem of coronal and root surface decay in elderly populations. As more teeth are retained and edentulism declines, more surfaces will be at risk in the adult population than ever before. The overall objective of this proposal is to reduce the extent of the caries process (in particular root surface caries) by primary and secondary prevention when the etiology of the disease has been clarified. By combining the information obtained in both the laboratory and clinic and refining the model system used to simulate the caries process, the ideal preventive and treatment strategies for root surface caries should be elucidated. This proposal intends to use both in vitro and in situ models to describe the disease process, and to determine the preventive agents most suited for use in root surface caries prevention. Specifically, we intend to (1) determine the level of fluoride needed to form root surface lesions with a mineralized surface layer, (2) test the hypothesis that remineralization occurs on remaining mineral and not demineralized matrix, (3) evaluate the resistance of remineralized lesion to further acid attack, (4) test whether fluoride present in the demineralizing or remineralizing cycle is most important, (5) determine the ability of existing fluoride agents to inhibit root surface caries in an in situ model. In vitro pH cycling experiments as well as the intraoral crown model assess episodic periods of demineralization and remineralization as opposed to continuous. The sensitivity of the single-section technique will allow before and after measurements on the same section. Both polarized light microscopy and microradiography will be used in qualitative and quantitative analyses. These studies should determine the usefulness of current fluoride preventive agents, and thus address the question of whether new and/or modified agents and vehicles are needed to efficiently prevent root surface caries.